033
FXUS65 KCYS 092153
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
353 PM MDT Sun Jun 9 2024

.KEY MESSAGES...

- There is a risk for a couple of strong thunderstorms in the
  vicinity of the Laramie Range this afternoon and evening.

- A more widespread threat for showers and thunderstorms will
  occur with a cold frontal passage on Monday afternoon and
  evening. A few storms may be severe.

- Mainly dry and rather warm conditions will prevail for Tuesday
  through Thursday, with increasing chances for showers and
  thunderstorms for Friday and Saturday, along with slightly
  cooler temperatures.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 400 PM MDT Sun Jun 9 2024

It`s a much quieter afternoon than yesterday, but not quite a blue
sky day. Moist southeasterly flow over the High Plains was able to
maintain a stratus deck into the early afternoon hours, which is
finally almost fully broken up at this time. Even though sunshine is
breaking through now, much of the areas east of I-25 is pretty
strongly capped. This is leading to lower overall storm coverage
compared to yesterday. However, an axis of uncapped and fairly
potent instability is still present along the Laramie range,
primarily in Albany and Converse counties. Low level southeast winds
have been able to pull deeper moisture up into the Laramie Valley,
holding the dryline in the western part of Albany county. This is
the primary zone of concern for strong thunderstorms today, and we
are indeed already seeing the best updrafts here. Storm motion
vectors are expected to be pretty slow, so some locally heavy
rainfall will be possible through the afternoon and early evening
hours today. Storms could also briefly produce large hail and/or
gusty winds. Any storms will probably struggle once they get east of
the Laramie range/I-25 as they run into the more capped environment.
A few additional showers and storms will remain possible through the
night, mainly north of US20. Continued moist southerly flow will
lead to some areas of patchy fog once again, but this time more
limited to the I-80 summit and I-80 corridor across Laramie county.

A more active weather day is expected for Monday as an upper level
shortwave approaches from the west. A rapid but brief period of warm
air advection will occur across the area tonight into Monday morning
ahead of this wave. Expect highs warmer than today especially east
of the Laramie range with a decent chance at 90F between Wheatland
and Scottsbluff. Expect storms to initially fire off the dryline in
Laramie/Goshen/Platte counties, but then get carried eastward more
rapidly once a potent surface cold front arrives later in the
afternoon. Forecast soundings show steeper lapse rates possibly
exceeding 8C/km and CAPE in the 1000-2000 J/kg range. The flow aloft
doesn`t look overly strong, but veering profiles atop southerly
surface flow will provide sufficient shear to get a few strong to
severe storms. HiRes models show fairly rapid upscale growth into a
more linear system by the time the convection reaches the eastern
side of the forecast area. Storms will be more progressive, but will
still include locally heavy rainfall. While the main line of storms
is expected to reach the eastern edge of the area around 5-7PM, we
will need to watch for some post-frontal convection developing later
in the evening hours as the front will actually increase low-level
moisture. Lastly, a trailing vort-max may keep the chance for
thunderstorms around through the night in zones north of roughly
US20.

Drier air works into the middle atmosphere on Tuesday, leading to
reduced precipitation chances. Storms should be confined to the
higher terrain and adjacent areas, and will be much more isolated
than preceding days. Expect temperatures some 5-10F above normal as
the ridge re-strengthens over the southwest CONUS. &&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Issued at 400 PM MDT Sun Jun 9 2024

Models in reasonable late this week and into next weekend. Hot
temperatures expected on Wednesday with all models showing a
flat upper level ridge over the Front Range and 700mb temperatures
of 15c to 18c across southeast Wyoming and western Nebraska
under westerly flow. With mostly sunny/partly cloudy skies,
expect high temperatures to peak in the mid 80s west of I-25,
and range from 90 to 95 degrees along and east of I-25 including
the western Nebraska Panhandle. May see a few late afternoon
showers or thunderstorms, but hardly any of this rain is
forecast to reach the ground, so kept POP below 15 percent for
most areas.

For later in the week, models show a backdoor shallow cool front
moving into the high plains for Thursday as the upper level
ridge axis amplifies northward west of the continental divide.
Not as warm on Thursday, but highs in the 80s to low 90s are
still expected. Very little moisture to work with on Thursday,
even as the shallow cool front moves south across the area, so
kept POP between 10 to 15 percent with a slight chance of
showers and thunderstorms in and near the mountains. Our next
forecast concern will be Friday and Friday night as models are
in good agreement on the movement and placement of a central
Pacific upper level low tracking northeast across southern
California and into Arizona and Utah. Will have to watch this
system since NAEFS is already showing 90th to 95th percentile
precipitable water values and low level east to southeast winds.
Deterministic models and ensembles showing a good chance for
some widspread moderate to heavy rainfall due to scattered to
numerous thunderstorms, mainly east of the Laramie Range. It`s
unclear what the severe potential is 6 days from now, but the
overall pattern is favorable for strong to severe thunderstorms.
Temperatures will trend cooler as we head into Friday and
Saturday, but still remain near seasonal averages.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 1140 AM MDT Sun Jun 9 2024

Low clouds and patchy fog will slowly lift and dissipate early this
afternoon for the western Nebraska terminals and KCYS through 20z. A
quick moving upper level ridge axis will be overhead today, and
combined with the low stratus, may greatly limit shower and
thunderstorm potential today and this evening.

HAZARDS/WEATHER TRENDS: Expect KCYS to hold onto IFR CIGS for the
next hour (19z) before low clouds lift and dissipate. VFR expected
after 20z for the rest of the afternoon and into the evening hours.
Some patchy fog or low clouds may reform tonight, but should primary
impact KCYS and KSNY with brief IFR possible towards sunrise Monday.

&&

.HYDROLOGY...
Issued at 400 PM MDT Sun Jun 9 2024

Warm temperatures are continuing to produce rapid snowmelt in the
high mountains of SE Wyoming. Warm to hot temperatures are expected
to continue through much of the week ahead, which will lead to
continued high flows along snowmelt fed rivers across the area. The
latest forecasts for the Encampment and upper North Platte Rivers no
longer show flood stage being reached in Encampment or Saratoga in
the coming days. These rivers should peak Monday morning below flood
stage. The Flood Watches/Warnings for those rivers have been
cancelled.

Plentiful runoff continues to come off of the Snowy range. Emergency
managers reported little change in flood impacts along the Little
Laramie River in Albany county. Therefore, decided to extend the
Flood Warning for another 24 hours. While the stage has receded
today, the typical diurnal cycle is expected to result in another
peak Monday morning. The Medicine Bow River near Elk Mountain also
remains at action stage. The latest crest this morning was just
below flood stage. Thus, extended the Flood Watch another 24 hours
as well.


&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

$$

SHORT TERM...MN
LONG TERM...TJT
AVIATION...TJT
HYDROLOGY...MN